Coronary guidewire system

ABSTRACT

A guidewire system configured for introduction into a body lumen, comprising a core wire having proximal end and a distal end and a tapering profile, and a micromachined tube coupled to the core wire, and a joint where the micromachined tube is joined to the core wire; the location of the joint being at a location on the tapering profile where the torsional force which can be transferred by the core wire and the micromachined tubing are substantially the same.

This application claims priority of U.S. Provisional Application No.60/171,383, filed Dec. 22, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to catheters and catheter guidewire apparatus andmethods for making same. More specifically, the present inventionrelates to a guidewire apparatus with improved torque and flexurecharacteristics.

2. State of the Art

Catheter guidewires have been used for many years to “lead” or “guide”catheters to target locations in animal and human anatomy. This istypically done via a body lumen, for example such as traversing Luminalspaces defined by the vasculature to the target location. The typicalconventional guidewire is from about 135 centimeters to 195 centimetersin length, and is made from two primary components—a stainless steelcore wire, and a platinum alloy coil spring. The core wire is tapered onthe distal end to increase its flexibility. The coil spring is typicallysoldered to the core wire at a point where the inside diameter of thecoil spring matches the outside diameter of the core wire. Platinum isselected for the coil spring because it provides radiopacity for betterfluoroscopic or other radiologic imaging during navigation of theguidewire in the body, and it is biocompatible. The coil spring alsoprovides softness for the tip of the guidewire to reduce the likelihoodof unwanted puncture of a luminal wall or the damaging of this and/orother anatomy.

As mentioned, navigation of a guidewire through the anatomy is usuallyachieved with the assistance of radiographic imaging. This isconventionally done by introducing contrast media into the body lumenbeing traversed and viewing the guidewire in the body lumen using X-rayfluoroscopy or other comparable methods. A guiding catheter can be used,as well as a catheter configured to perform a procedure and to bedirected to the target location by the guidewire. Catheters to performcoronary angioplasty and/or deploy stents are examples.

The guidewire is provided with a tip that is curved or otherwise bent toa desired angle so as to deviate laterally a relatively short distance.By rotation of the wire, the tip can be made to deviate in a selecteddirection from an axis of the guidewire about which it rotates. Thecatheter is advanced over the guidewire or the guidewire is insertedinto a catheter so that the guidewire and the catheter cooperate toreach the target location. The guidewire can be advanced so that itsdistal end protrudes out the distal end of the catheter, and also pulledback in a proximal direction so as to be retracted into the catheter.The catheter enables introduction of contrast media at the location ofthe distal tip to enable the visualization of a Luminal space beingtraversed by the catheter and guidewire. The guidewire orcatheter/guidewire combination are introduced into a luminal space suchas a blood vessel and advanced therethrough until the guidewire tipreaches a desired luminal branch. The user then twists the proximal endof the guidewire so as to rotate and point the curved distal tip intothe desired branch so that the device may be advanced further into theanatomy via the luminal branch. The catheter is advanced over theguidewire to follow, or track, the wire. This procedure is repeated asneeded to guide the wire and overlying catheter to the desired targetlocation. The catheter accordingly provides a means to introducecontrast media, and also provides additional support for the wire. Oncethe catheter has been advanced to the desired location, the guidewiremay be withdrawn, depending upon the therapy to be performed.Oftentimes, such as in the case of balloon angioplasty, the guidewire isleft in place during the procedure and can be used to exchangecatheters.

As is known, a guidewire having a relatively low resistance to flexureyet relatively high torsional strength is most desirable. As theguidewire is advanced into the anatomy, internal frictional resistanceresulting from the typically numerous turns and attendant surfacecontacts, decreases the ability to turn the guidewire and to advance theguidewire further within the luminal space. This, in turn, may lead to amore difficult and prolonged procedure, or, more seriously, failure toaccess the desired anatomy at the target location and thus a failedprocedure. A guidewire with high flexibility helps overcome the problemscreated by this internal resistance. However, if the guidewire does notalso have good torque characteristics (torsional stiffness), the userwill not be able to twist the proximal end in order to rotate the distaltip of the guidewire to guide its advance as required.

Among the approaches suggested in the prior art for increasing theflexibility of the tip of a guidewire is that of cutting axially spacedgrooves in and near the tip, with the depths of the grooves increasingtoward the tip. See, for example, U.S. Pat. No. 5,437,288. Increasingthe flexibility of a tubular member for use in catheter applications bymaking cuts therein is also known. The use of cuts to increaseflexibility on one side only of a tubular guidewire is disclosed, forexample, in U.S. Pat. No. 5,411,483. However, these prior art approachesdo not inform the art how to increase the flexibility of the guidewirewithout also significantly diminishing its torsional stiffness. Theresult can be a guidewire with a machined portion that is very flexible,but which also has very low torsional strength.

SUMMARY OF THE INVENTION

It has been recognized that it would be desirable to have a guidewirethat is very flexible at its distal tip, yet which retains a relativelyhigh degree of torsional stiffness, facilitating its use andmanipulation.

A catheter guidewire apparatus in accordance with principles of theinvention comprises a thin elongate body of material having anlongitudinal axis, and which is formed so as to define at a proximalportion a wire, and at a distal portion a configuration comprising aplurality of integrally formed beams disposed along the length of thethin elongate body. The integral beams extend axially and transverselyof the body and are positioned and formed to give the guidewireflexibility while maintaining a relatively high degree of torsionalstiffness. By manipulating the size, shape, spacing, and orientation ofthe beams, the torsional stiffness of the guidewire relative to itsflexibility or beam stiffness can be selectively altered. These beamscomprise the portions of the wall of a tubular body, or the outerportions adjacent the outer surface of a solid body member, which remainafter cuts are machined into the body.

In more detail, in order to optimize the performance of the guidewiretransverse and axial beams adjacent one to another are configured sothat the strain (deformation) in the adjacent axial and transverse beamsas defined above is as nearly as possible equal in magnitude when theguidewire is subjected to torsional and bending forces resulting fromtwisting and bending of the apparatus. The resistance to fatigue failureof the axial and transverse beams can also be matched, since a procedurecan involve numerous repetitions of deformation of the beam elements asthe guidewire is turned and advanced in tortuous anatomy, and thedeformations can be large, this is also a good methodology to optimizeperformance. Combining the methods, and/or using the one that yields thebest performance for a particular application results in improvedperformance over prior guidewires.

In a further more detailed aspect, the beams can be formed between cuts,by making cuts in pairs substantially opposite from one another andsubstantially parallel to each other. The spacing and depth of the cutscomprising the cut pairs being adapted to provide desired maximumflexibility while sacrificing minimal torsional strength.

In further detail, the elongate member with beams formed therein can bepolished and corners rounded to minimize stress concentrations andincrease resistance to fatigue.

Other features and advantages of the invention will be apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, fragmented, partially crossectional, view of oneembodiment of a catheter guidewire apparatus configured in accordancewith the principles of the present invention;

FIG. 2 is a side, fragmented, view of a portion of a guidewire showingdifferent types of cuts or etchings which may be utilized in a solid ortubular guidewire in accordance with principles of the presentinvention;

FIG. 3 is a side, fragmented, view of the tip of a guidewire withradiopaque coil or band wrapped thereabout, in accordance withprinciples of the present invention;

FIGS. 4 and 5 show side, fragmented views of two embodiments ofguidewires formed with cuts, in accordance with principles of thepresent invention;

FIG. 6 is a side, fragmented view of a tapered guidewire formed withcuts, in accordance with principles of the present invention;

FIG. 7 is a side, fragmented view of a solid guidewire formed with acoiled tip, in accordance with principles of the present invention;

FIG. 8 is a graph of guidewire tensile strength compared to bendingstiffness for a micromachined guidewire in accordance with principles ofthe present invention;

FIG. 9 is a graph of the ultimate torsional strength of a micromachinedguidewire in accordance with principles of the present inventioncompared to its bending stiffness;

FIG. 10 is a graph of the torsional stiffiess of a micromachinedguidewire in accordance with principles of the present inventioncompared to its bending stiffness;

FIG. 11 is a graph showing the ratio of torsional stiffness to bendingstiffness of a micromachined guidewire in accordance with principles ofthe present invention compared to its bending stiffness;

FIGS. 12a, 12 b, and 12 c show cross-sectional views of guidewiresdisposed within lumens of circular and elliptical catheters;

FIG. 12d shows the potential serpentine path of a guidewire through acatheter which tends to wedge the guidewire within the catheter;

FIG. 13 shows a perspective, partially fragmented, view of a guidewirein accordance with principles of the invention in another embodiment;

FIG. 14 shows a side view, partially fragmented, of a core wire of theguidewire of FIG. 13 illustrating the grind profile;

FIG. 15 shows a side view, partially fragmented, of a core wire of theguidewire of FIG. 13 with a medial stainless steel wire coil added;

FIG. 16 shows a side view, partially fragmented, of a core wire of theguidewire of FIG. 13 with a medial wire coil and distal marker coiladded;

FIG. 17 shows a side view, partially fragmented, of a core wire of theguidewire of FIG. 13 with a medial wire coil and distal marker coil andproximal stainless coil added;

FIG. 18 shows a side view, partially fragmented, of a core wire of theguidewire of FIG. 13 with a medial wire coil, distal marker coil,proximal stainless coil and micromachined tubing added at a distal tipportion;

FIG. 19 shows a fragmentary perpsective view of a portion of amicromachined tubing segment such as shown in FIG. 18, in accordancewith principles of the invention;

FIG. 20 shows a crossectional view, taken along line 20—20 in FIG. 19 ofthe micromachined tube shown in FIG. 19;

FIG. 21 shows a fragmentary perpsective view of a portion of amicromachined tubing segment such as shown in FIG. 19 subjected totorsional forces, illustrating deformation of the tubing;

FIG. 22 shows a cut orientation distribution progressing in an axialdirection along a micromachined guidewire segment;

FIG. 23 shows a fragmentary side view of a portion of a micromachinedtubing segment illustrating a cut orientation distribution in anotherembodiment; and

FIG. 24 shows a diagram further illustrating the cut set distributionshown in FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to FIG. 1 of the drawings which illustrates oneembodiment of a solid guidewire 200 made in accordance with the presentinvention. The guidewire 200 includes a proximal end 204 a distal end208, and a midportion 210 disposed therebetween, with the proximal endbeing mounted in a conventional pin vise type torquing chuck 212. Theguidewire 200 is preferably constructed of a material including nickeltitanium alloy, and may range in size from about 0.008 inches to about0.090 inches in diameter and from about 135 to 300 centimeters inlength. The guidewire 200 can also be made of other materials, forexample stainless steel. Four conventional preferred diameter sizes are0.008 inches, 0.014 inches, 0.016 inches and 0.035 inches.

Cuts, slots, gaps or openings 216 and 220 are formed in the guidewire200 along the length thereof, including the midportion 210, either bysaw cutting (e.g., by a diamond grit embedded semiconductor dicingblade), etching (for example using the etching process described in U.S.Pat. No. 5,106,455), laser cutting, or electron discharge machining. Thecuts 216 are angled to allow for a longer cut and thus greaterflexibility, whereas cuts 220 are generally perpendicular to thelongitudinal axis (long dimension) of the guidewire.

As will be discussed in more detail below, the cuts are specificallyconfigured to form transverse and axial beams therebetween within thebody of the guidewire. This configuration allows the cuts and beams tointeract to provide for lateral flexibility in the guidewire, whilemaintaining improved torsional stiffness. By controlling and varying thespacing, depth and type of cuts, the flexure profile and torsionalstiffness of the guidewire may be selectively and relativelyindependently modified. Generally, the more closely spaced the cuts andthe greater their depth, the more flexible will be the guidewire.However, modification of the exact shape, orientation, and spacing ofthe cuts will also allow selective modification of flexibility whilepreserving the desired torsional characteristics of the member.

The distal end 208 of the guidewire 200 may be preshaped with a curve,as shown, to allow for directing the guidewire around curves and bends.To maintain flexibility in the distal end 208, cuts may also be providedon that end. Advantageously, the tip is rounded to minimize the chanceof trauma to body tissue. Also formed on the distal end 208 is aradiopaque marker or band 224. The band 224 may be gold or platinumalloy (for X-ray fluoroscopy) or gadolinium or dysprosium, or compoundsthereof (for MRI) and may be formed on the distal end 208 by deposition,wrapping or use of shape memory alloy (NiTi) effect to “lock” the bandin place around the end.

With reference to FIG. 2 illustrating a portion of another exemplaryguidewire 230, three different examples of types of cuts 234, 238 and240 can be appreciated. These types of cuts provide a kind of built-inflexure “stop” to prevent further flexure of the guidewire when sides ofthese cut openings close to contact one another and prevent furtherflexure in that direction. Wedge shaped cuts 234 may be formed onopposite sides of the guidewire 230, with the greater width of the wedgebeing at the bottom of the cut. T-shaped cuts 238 may likewise be formedon opposite sides of the guidewire 230, with the cross piece of the Tbeing at the bottom of the cut. Cuts 240 are generally circular asshown. It will be apparent that other cut shapes could also be providedto meet the needs of the user. The cuts 234, 238, and 240 are shownoppositely oriented, but it will be apparent that the cuts could also beformed at circumferentially-spaced locations about the guidewire, or atalternating locations such as shown and described in more detail withregard to, for example, FIG. 5.

All three types of cuts shown in FIG. 2 form an integral axial beamsection, shown in cross-hatch as areas 232, 236, and 242, respectively,between oppositely disposed cuts. This configuration provides at leasttwo distinct benefits. First, it allows the beam section to be longerthan the gap of the flexure stop. This allows the amount of strain inthe beam prior to stop engagement to be controlled by varying the ratioof beam length to gap size, allowing more flexibility, i.e. less bendingresistance.

However, the location and shape of the beam section 232, 236, or 242also greatly influences the torsional characteristics of the guidewire230. As is well known by those skilled in mechanics, torsional strengthis primarily provided by the outer portion of the cross section of amember. Thus, for illustration, a relatively thin-walled pipe will havenearly the same torsional strength as a solid bar of the same diameterbecause the central portion of the cross section of the solid barcontributes relatively little to torsional strength. Similarly, inproviding an axial beam which crosses the entire cross-section of theguidewire 230, the portion of the beam sections 232, 236, or 242comprising the outer portion of the cross section of the guidewire aremost important in efficiently transmitting torque. Also, the axial beamsare more or less effective in transmitting torsional forces from oneside to the other of the cuts 234, 238, and 240 depending on theirshape.

For example, beam 232 is relatively long (measured in the direction ofthe long axis of the guidewire), but is relatively deep (measuredtransverse to the long axis) and will therefore transmit a relativelylarge amount of torsional force. Beam 236 is longer and thinner thanbeam 232, and will therefore transmit a smaller amount of torsionalforce across the cut 238. Of the examples given in FIG. 2, beam 242 isthe shortest and configured to transmit the greatest amount of torsionalforce. However, given the size and shape of cuts 240, this configurationmay provide the greatest flexibility. Because the small flexure stopgaps of cuts 234, 238, and 240 may be varied in width without changingthe depth or overall shape of the cut, the flexibility of the guidewiresection may be selectively altered without affecting the size orstrength of the axial beam section. Thus, the flexibility and torsionalstrength of the guidewire may be selectively and relativelyindependently altered.

Advantageously, longitudinally adjacent pairs of cuts may be rotatedwith respect to each other by about 80-90 degrees around the axis of thewire provide flexure laterally in multiple directions. However, the cutsmay be located to provide preferential flexure in only one, two, three,etc. directions, if that is desired. Of course, the cuts could berandomly formed to allow bending (flex) equally, non-preferentially inall directions or planes. This could be achieved by circumferentiallyspacing the cuts.

FIG. 3 illustrates an alternative embodiment for applying a radiopaquemarker to the distal end of a guidewire 244, shown in side, fragmentedview. An annular trough or channel 248 is formed at the tip of theguidewire 244, and a radiopaque wire coil, preferably made of platinumalloy, is wound about the guidewire in the channel. The coil 252 couldbe welded or soldered to itself and/or the guidewire to hold it in placeat the tip of the guidewire 244. If, in an alternate example, a gold orplatinum band rather than a coil is used with a nickel titanium alloyguidewire, the guidewire could be cooled and deformed to allow the bandto be placed on the wire and then when the guidewire is returned to roomtemperature, the band would be maintained in place on the guidewirewithout the need for welding or soldering or other joining mechanism.The same is true for a coil, except forjoining the coil to itself.

FIG. 4 is a side, fragmented view illustrating a solid guidewire 260formed with opposing cuts 262, 264 spaced along a portion of theguidewire, and opposed cuts 266, 268 rotated 90 degrees from saidopposed cuts 262, 264. As with cuts 262, 264 the rotated cuts 266, 268are preferably arranged in opposing pairs, with opposite cut 266corresponding to 268 not visible on the far side of the guidewire. Ofcourse, the cuts could be formed to provide preferential bending (flex)in one plane, or could be positioned to allow bending in multipleplanes. This could be achieved, for example, by rotating adjacent pairsof cuts by 45 degrees with respect to one another or some other selectedangular amount 0-90 degrees. Also shaded in FIG. 4 are the transversebeam sections 263 between adjacent opposing cuts 262, 264. It will beapparent that the pairs of rotated cuts 266, 268 will also formtransverse beams therebetween, except that these beams will be orientedat an angle of 90 degrees relative to the beams 263.

FIG. 5 is a side, fragmented view of a solid guidewire 270 formed withstaggered or offset cuts 274, 275 on opposite sides of the guidewire. Acurved distal end 278 is also includes a radiopaque marker band 280. Aswith the FIG. 4 embodiment, certain pairs of offset cuts could berotated with respect to the other pairs, to thereby control direction offlexure. This configuration also presents particular advantagesregarding torsional control. As is evident from FIG. 4, opposed cutsproduce thin flexure transverse beams 272 between each pair of opposedcuts. The dimensions and flexure properties of these beams aredetermined by the depth and separation of the cuts and so theflexibility of a guidewire with opposed cuts may be controlled byvarying these parameters as well as the width of the cuts.

Offset cuts, as indicated in FIG. 5, produce much larger flexure beams272 in the area between each pair of adjacent cuts. As will be expected,these large beams are able to transmit a relatively large amount oftorsion. Depending on the depth of the cuts 274, this section will alsocomprise relatively thin axial beams 276 between the base of each cutand the opposing side of the guidewire.

It will be apparent that the flexure properties of this guidewire aredetermined not only by the depth and width of the cuts (as with opposedcuts) but also by the offset (axial spacing) of the cuts. Consequently,the flexibility of a guidewire with offset cuts can be controlled byvarying any or all of these parameters. Also, the flexibility could bevaried simply by controlling the degree of the offset while keeping thedepth and width of the cuts constant.

FIG. 6 is a side, fragmented view of a solid guidewire 284 having anenlarged proximal section 288, which provides more torquability, and anarrowed distal section 292, covered by a hydrophilic polymer sleeve294. For example, the enlarged section could be 0.014 inches in diameterwhereas the narrowed section could be 0.010 inches in diameter. Thedistal end 296 of the guidewire 284 is formed with cuts as earlierdescribed. Of course, cuts could also be provided at other locations inthe narrowed section 292 or in the enlarged section 288, to increaseflexibility, while maintaining high torsional stiffness.

FIG. 7 is a side, fragmented view of a solid guidewire 300 having atapered distal end 304 about which is wrapped a coil 308 made, forexample, of platinum alloy. Disposed at the tip of the distal end 304 ofthe guidewire and in the end of the coil 308 is a solder ball 312. Cuts316 may also be formed in the guidewire 300 as discussed earlier. Inaddition to the use of cuts to control the flexure of a guidewire,nickel titanium alloy guidewires can be heat treated to vary the flexurecharacteristics. For example, selective annealing along the length ofthe wire can change stress/strain relationship of the material, and thusthe flexure.

In the embodiments of a solid guidewire discussed above, the guidewirescan be made “flow directable” by providing highly flexible distal ends.“Flow directability” means that the distal end of the guidewire tends to“flow” with the blood around curves and bends in a vasculaturepassageway. To reduce resistance to movement of a guidewire in avasculature passageway, the surface of the guidewire may beelectropolished to increase the smoothness thereof, and additionally, alubricious coating may be applied to the surface of the guidewire—suchcoatings might illustratively include silicone based oil and/or polymeror hydrophilic polymers. Alternatively, a lubricious sleeve made, forexample, of a hydrophilic polymer could also be provided for disposalover the guidewire. Such polishing has the additional benefit ofincreasing fatigue failure resistance.

FIGS. 8-11 provide graphical representation of the improvement thisinvention provides over conventional prior art devices. These graphsdepict comparative test results of catheter guidewires formed accordingto this invention, showing the strength of catheter guidewires inaccordance with principles of the invention compared to prior artdevices, and the relative preservation of torsional strength relative toflexibility.

FIG. 8 is a graph of guidewire tensile strength compared to bendingstiffness for the micromachined guidewire of the present invention. Theindividual (square) data points represent tension test results formicromachined guidewires. The ultimate tensile strength in pounds isindicated on the vertical axis, while the bending stiffness in psi isgiven on the horizontal axis. Below the horizontal axis is a second axisnoting the size of stainless steel wire which would correspond to therespective bending stiffness shown in the horizontal axis. The solidline represents the theoretical tensile strength for equivalent solidwires.

This figure shows that micromachining cuts in the surface of theguidewire does not significantly reduce its tensile strength compared tonon-machined guidewires for the same lateral bending stiffiess. This isan important consideration in the catheter field because lower tensilestrength could increase the likelihood of breakage of the guidewireduring a procedure, or while attempting to extract the guidewire from apatient compared with conventional wires.

FIG. 9 is a graph showing ultimate torsional strength of themicromachined guidewire of the present invention compared to its bendingstiffness. The vertical axis shows the ultimate torsional strength ofthe guidewire in units of pound-inches, and the horizontal axis showsthe bending stiffness in psi. As with FIG. 8, the square data pointsrepresent actual test results of micromachined catheter guidewires, andthe solid line represents the theoretical results for a catheterguidewire of solid circular cross section. It will be apparent from thisgraph that as the bending stiffness (or size) of the conventionalguidewire decreases, the expected or theoretical torsional strength alsodecreases. This is depicted by the solid line. However, as the actualtest results indicate, as the size or bending strength of themicromachined guidewire decreases, the torsional strength does notcorrespondingly decrease as would be expected. Instead, as can be seenfrom the divergence of the data points from the solid line, thetorsional strength of the guidewire decreases at a much slower rate.This situation is depicted in a slightly different way in FIG. 10, whichprovides a graph of the bending stiffness of the micromachined guidewireof the present invention compared to its torsional stiffness in psi.Again, the actual results diverge from the expected results for smallerand more flexible guidewires.

The importance of this situation is most clearly evident from FIG. 11,which is a graph showing the ratio of torsional stiffness to bendingstifftess of the micromachined guidewire of the present inventioncompared to its bending stiffness. In this graph the vertical axisrepresents a ratio of torsional stiffness to bending stiffness (JG/EI),with the result that the expected relationship of bending stiffness totorsional stiffness (the solid line) is now a horizontal line. In FIG.11, this line is set equal to unity, in order to more graphically showthe actual results of the inventors' tests. As can be seen from theseactual test results, as the flexure strength decreased, the torsionalstrength of the micromachined guidewires was more than 30 times morethan expected.

The condition indicated by FIG. 11 represents some unexpected results.When the inventors first began micromachining catheter guidewires, aswith the prior art, the goal was primarily to increase the flexibility.However, as guidewire sizes decreased and/or flexibility increased, theinventors noticed a corresponding (and expected) decrease in torsionalstrength. This is a significant problem with catheter guidewires becauseguidewires with low torsional strength cannot be manipulated as easily,and are more likely to become wedged or jammed into the catheter orvasculature of the patient. With a torsionally weak guidewire, when theuser twists the proximal end, there is a significant delay in thetransmission of the torque to the distal end. Indeed, like axiallytwisting the end of a weak coil spring, most of the torque is nottransmitted at all. Instead, the geometry of the guidewire is likely tobe deformed into a serpentine shape and wedge into the side of thecatheter or vasculature in which it is located.

FIG. 12 shows cross-sectional views of guidewires disposed within thelumen of circular and elliptical catheters. As will be apparent, when acircular catheter is advanced into the vasculature of a patient andnavigates curves and other tortuous routes, the cross-sectional shape ofthe catheter frequently tends to flatten out in places into a moreelliptical cross-section. When a guidewire 400 is disposed in catheter402 having a circular cross-section, it would have no preference as toits location within the cross section—its position will present a stateof physical equilibrium regardless of its location because all locationsare the same. However, with an elliptical catheter 404, the guidewire400 in a central location represents a state of unstable equilibrium,like a ball sitting on the top of another ball. The result is that theguidewire will naturally gravitate to a point of stable equilibrium 406,in the tight corner of the catheter lumen. In this condition, it can beseen that the area of contact between the guidewire and the catheter ismuch larger, resulting in large frictional forces which will hinder theeasy movement of the guidewire within the catheter.

This condition will also tend to wedge the guidewire within the cathetersimply by virtue of the serpentine shape. FIG. 13 shows the potentialserpentine path of a torqued guidewire 420 through a catheter 422. Byvirtue of the deformation of the guidewire 420, when an axial drivingforce (denoted Fwire in FIG. 13) is applied to the guidewire 420, itwill be converted into an axial force (denoted Faxial) and aperpendicularly oriented wedging force (denoted Wedging Force) whichwill tend to jam the guidewire within the catheter.

To prevent these problems, the inventors experimented with methods ofproviding cuts in catheter guidewires that would increase flexibilitywithout reducing torsional strength as much. It was hoped that for aguidewire of a given flexibility, the torsional strength could beincreased by 50% above the theoretical or predicted torsional strength.After trying many configurations, the inventors discovered that formingcuts in the guidewires so as to create beams with a particular locationand configuration would allow flexibility to be increased without acorrespondingly large decrease in torsional strength. The inventors werepleasantly surprised when testing the present invention to find thatinstead of a 50% increase of torsional strength, they had found a way toprovide a more than 3000% increase in torsional strength. As a result,guidewires formed by the present method provide significantly greatertorsional strength relative to their flexibility than the prior art.

With reference to FIG. 13 an exemplary guidewire 500 in accordance withprinciples of the invention, and giving the advantages discussed above,comprises a proximal portion 502 extending from a proximal end 504 to afirst transition portion 506 where the diameter of the guidewirechanges. This proximal portion comprises a stainless steel core wire 501configured as solid wire of circular cross section. The core wire in theproximal portion is covered with a low friction coating. For examplePTFE is used to coat the proximal portion in the illustrated example.The proximal portion has a diameter as large as needed to transmittorque sufficient for the intended use of the guidewire. For coronaryand some peripheral uses, for example, a diameter of about 14thousandths of an inch is appropriate, and is used in the illustratedexample.

At the first transition portion 506 the stainless steel wire is groundto a smaller diameter, transitioning over an axial length sufficient toprovide a smooth transition. This is about 2 inches in one embodiment.Beginning at a distal end of the first transition portion the guidewire500 has a more complex configuration. A proximal coil 508 is disposedover the stainless core wire 501. The core wire continues to the distalend 510 of the guidewire, the proximal coil overlaying the core wire aswill be further explained. The proximal coil is attached to the corewire at the first transition portion 506 by a proximal solder joint 512at a point where the inner diameter of the coil matches the outerdiameter of the core wire. The diameter of the core wire continues todecrease under the proximal coil, and beyond it in accordance with agrind profile that will be described below.

At a distal end of the proximal coil 508 the guidewire 500 in anexterior aspect comprises a micromachined tubing 514 formed of amaterial comprising a superelastic material such as NiTi alloy. Thismicromachined tubing is very important to functionality of the catheterguidewire, as it transmits torque to the distal end 510 of the guidewirebut is very flexible. The micromachined tubing overlays additionalstructure as will be described below. The micromachined tubing isattached to the proximal coil 508 via other underlying structure, andthe core wire 501 at a medial solder and glue joint 516. The location ofthis joint is important as it is the point where the torsional force“carrying capacity” of the core wire 501 is substantially equal to thatof the micromachined tubing. A force path is therefore established whichextends through the core wire from the proximal end 504 of the guidewire500 to the medial solder and glue joint 516, then continues through themicromachined tubing 514 to the distal end 510 of the guidewire 500.

As can be appreciated, the view of FIG. 13 is fragmented, and not toscale. The outer diameter of the proximal coil 508 is substantially thesame as the proximal portion 502 of the core wire. The outer diameter ofthe micromachined tubing 514 at the distal tip portion 511 of theguidewire 500 is also approximately the same, all being about 14thousandths of an inch. In one embodiment the proximal coil is about 11inches long and the distal tip portion comprising the micromachinedtubing is about 2 inches long. The distal tip portion can be given acurved or other bent configuration is known in the art.

At the distal end 150 of the guidewire 500 the micromachined tubing,underlying structure (not shown), and the core wire 501 are attached ata distal solder and glue joint 518. The core wire has a very smalldiameter at the distal end, the grind profile reducing it toapproximately 2 thousandths of an inch prior to reaching that point. Thedistal solder and glue joint comprises an adhesive 520 which is formedinto a rounded configuration at the distal end of the guidewire to forman a-traumatic tip.

Turning to FIGS. 14-18 the construction of an exemplary guidewireconfiguration will be described in more detail. With referenceparticularly to FIG. 14, the core wire 501 alone is seen to advantage,with the grind profile appreciable. The corewire has a roundedconfiguration at the proximal end 504 of the wire, and the proximalportion 502 is as previously described, and is about 65 inches in lengthin one exemplary embodiment. The grind profile extends about 14 inchesfurther to the distal end 510 of the guidewire 500. In addition to thefirst transition portion 506, a second 522, and a third 524, transitionportion are provided. Distal of the first transition, which as mentionedis about 2 inches in length in the exemplary illustrated embodiment, thecore wire has a first reduced diameter portion 526 having a length ofabout 6 inches and a diameter of about seven and a half thousandths ofan inch. The second transition portion is also about 2 inches in length,and the diameter further reduces from that of the first reduced diameterportion to about five and a half thousandths of an inch. This diameteris maintained for about two and a half inches, to form a second reduceddiameter portion 528. At the third transition portion 524 the diameterfurther decreases to about two thousands of an inch, which is maintainedto the distal end 510 as mentioned, to form a third reduced diameterportion 530. This third transition portion is about one tenth of an inchin length, and the third reduced diameter portion is about one and ninetenths inches in length in the illustrated exemplary embodiment. Thethird reduced diameter portion is configured to be extremely flexible aswill be appreciated, but retain sufficient axial strength to helpprevent distal tip separation on withdrawal of the guidewire from aposition where the tip may be stuck in the anatomy, and to assist infacilitating pushability of the distal tip portion 511 of the guidewire.

With reference to FIG. 15, the underlying structure mentioned beforewill now be described. A medial coil 532 is attached to the core wire501 at the third transition portion 524. The medial coil has an outerdiameter substantially equal to the inner diameter of the proximal coil508 and the inner diameter of the micromachined tubing 514. It isattached by soldering, and this location of attachment on the thirdtransition portion is that of the medial solder and glue joint mentionedabove. Also, it will be noted that the location is near the proximal endof the third transition portion, so that the diameter of the core wireat this location is substantially the same as the second reduceddiameter portion 528. As the core wire transfers torque to themicromachined tubing at this location as mentioned above, the locationon the grind profile is important as it represents the “end of the line”for torque transmission through the core wire, and the diameter of thecorewire is directly proportional to the amount of torsional force thatcan be transmitted, the location and diameter are chosen in conjunctionwith selection of the parameters of the micromachined tubing so that the“carrying capacity” for torque is substantially equal. A mis-matchrepresents an inefficiency in this regard and is to be avoided unlessfor some design objective a discontinuity in torquability is desired atthis point.

The medial coil 532 is formed of stainless steel in one embodiment, andhas a proximal unwound portion 534 at its proximal end, to aid in moresecure bonding to the core wire 501 as a longer length of coil wire canbe bonded due to slight deformation thereby allowed to follow the grindprofile. The medial coil has a distal unwound portion 536 which will befurther described next below.

Turning to FIG. 16, a distal coil 538 is disposed over the third reduceddiameter portion at the distal tip portion. The proximal end of thedistal coil is provided with an unwound portion 540 which cooperateswith the distal unwound portion 536 of the medial coil to form a secureinterlock by intertwining of the coils, then soldering. As will beappreciated the distal coil can be of slightly larger diameter wire, dueto the reduced grind profile it overlays, but the outside diameter isheld to be slightly less than that of the inside diameter of themicromachined tubing (not shown) as will be described. The distal coilis formed of a radiopaque material in the illustrated embodiment toprovide enhanced fluoroscopic visibility. Materials such as platinum,gold, palladium, dysprosium, as known in the art, are used for thispurpose, and accordingly the increased diameter wire used provides moreradiopacity when formed of such a material useful for this purpose. Thedistal coil thus acts as a marker to aid in navigation of the guidewirewithin the anatomy of a patient. As will be appreciated, the drawingfigures are not to scale, and the distal coil can be considerably longerthan the medial coil 532. The distal end of the distal coil is solderedto the core wire 501 adjacent the distal end 510 at the location of thedistal solder and glue joint 518.

With reference to FIGS. 14, 15, 16, and 17, it will be appreciated thatthe guidewire 500 apparatus is assembled by attaching the medial spring532 to the core wire, then attaching the distal (marker) coil 538 to themedial coil, then the proximal coil is slipped over the assembly andsoldered to the core wire 501 at the proximal solder joint 512 and tothe medial coil 532 at the location of the medial solder and glue joint516. The solder used throughout is a silver or gold alloy solder oranother material regulatory-approved for such use.

With reference to FIG. 18, fabrication of the catheter is completed byplacement of the micromachined tubing 514 over the distal tip portion511. It is fixed in place by securing it at its proximal end at themedial solder and glue joint 516 by means of a suitable adhesive such asa UV cured regulatory-approved adhesive such as Dymax, and by attachingthe distal end to the distal tip of the core wire 501, and also to thedistal (marker) coil by an identical or similar adhesive. As mentionedthis adhesive when cured forms a rounded tip 520 to reduce trauma, andcompletes the distal solder and glue joint which holds together the corewire, distal marker coil, and the micromachined tubing at the distal end510 of the guidewire.

The guidewire can further include a micromachined “barcode”identification 142 located at a convenient location such as adjacent theproximal or distal end of the guidewire. The barcode is made by verylightly scoring the surface to form a binary code to encode identifyinginformation regarding the catheter. This is done by a similar process tothat used to micromachine the tubing 514 or another guidewire asdiscussed above and as follows. The advantage of such a marking systemis that individual guidewires can be identified, enabling “lot of one”custom manufacturing and marking of one to as many as desired guidewires500.

Turning now to FIG. 19, discussion of the micromachined tubing 514 morespecifically should include mention of how the tubing is made. Inaddition to the description above with regard to wires generally, andbelow with regard to this tubing segment specifically, further detailsregarding fabrication of the tubing can be found in copending U.S.patent application Ser. No. 09/470,606, the disclosure of which ishereby incorporated herein by reference.

As will be appreciated, enhanced performance is obtained by optimizationof one or more physical attributes of the guidewire. In the case of theillustrated exemplary embodiment now being discussed, a uniqueconstruction combined with optimization provides increased torquabilitywhile allowing flexure, so as to be compliant with tortuous vasculaturein accessing a target site within the patient's anatomy.

For the moment digressing to review of a more general case, as mentionedabove when a member of circular cross section is used to transmit atorsional force, the overwhelming majority of the force is “transmitted”by the outer portions of the member, the capacity to resist deformationdue to induced stress being maximum at the outer circumferential surfaceof the member. Accordingly, whether a tubular member or a solid memberof circular cross-section of a given material is used to transmittorque, relatively little increase in diameter for the tubular member isrequired to transmit the same amount of torque because in fact the“middle” portion of a solid circular member contributes comparativelylittle to resistance of the stresses, and hence does little to transmitthem.

The present invention is directed to maximizing torque transmission,while minimizing resistance to bending of a guidewire body, for examplein the tubular member 514 shown. To do so, from the forgoing it will beapparent that only the equivalent of a tubular structure is implicated,even though a solid member may be used. Therefore the followingdiscussion will apply to solid wires as well, though it will beunderstood that this is because an assumption is made that the innerportion of the wire is not contributing appreciably, and the structureother than a tubular portion of it is being ignored. In practice atubular configuration is advantageous as other structure can be placedinside, as in the case of the illustrated embodiment given by exampleherein employing a tubular micromachined tubing segment 514 at a distaltip portion 511.

One way in which the guidewire distal portion is optimized is usingsuperelastic material, preferably formed as a tube, micromachining thetube to create a structure which maximizes torque transmission whileminimizing resistance to bending. A section of micromachined tubing 514,having slot-like cuts formed therein is shown to illustrate thestructure. The cuts are opposed cuts in the illustrated embodiment. Thatis, two cuts are made from opposite sides of the tubing at the samelocation along the longitudinal axis of the tubing. The depth of thecuts is controlled to leave a segment 546 of the tubing wall extantbetween the cuts on each of the opposite sides (180 degrees apart) ofthe tubing. These segments will acts as “beams” as discussed above tocarry forces across the cut area at that location along the longitudinalaxis 548 of the tubing. As a matter of convention such segments will bereferred to as “axial beams” 546 as they are disposed to carry ortransfer forces in roughly an axial direction from adjacent structure onone side to adjacent structure on an opposite side. When a pair ofopposed cuts 550 is made adjacent to the cuts previously described (544)the location of the cuts is made such that the axial beam(s) 546A formedby the second set of cuts is displaced circumferentially from theadjacent axial beam(s) 546. This of course is done by rotation of thetube through some angle relative to the saw used to cut the tubingbefore cutting. This can be seen in FIG. 20. The amount of rotation isselected with each successive cut to give a pattern calculated tofacilitate torque transmission while also facilitating bending of thetube after machining and to mitigate whipping. The specifics of thiscutting distribution will be discussed below. With reference again toFIG. 19, what is important to this discussion is that in addition toaxial beams, other beams, which by convention we call transverse beams552 are created.

The transverse beams 552 are defined in this example as the curvedportion of the tubing wall between adjacent cuts 544, 550 and adjacentaxial beams. e.g. 546 and 546A. As will be appreciated, these transversebeams carry forces from a particular set of axial beams to the twoadjacent axial beams created by an adjacent set of cuts.

With reference to FIG. 21, as will be appreciated once a tube 514 hasbeen fabricated and a torquing force is applied at one end, say theproximal end, with respect to another, say the distal end, the forces inthe machined tube will tend to deform the axial and transverse beams,e.g. 546 and 552. In order to optimize the machined tube for maximumtorque transmission, the goal is to match, insofar as possible, thestrain in the axial and transverse beams all along the length of thewire. This is so that one or the other will not constitute a weak pointwhich will fail by deformation well beyond that of the adjacent axial ortransverse beams when the torquing force is applied. As can beappreciated, with reference to FIG. 19 this matching can be done intubing of constant cross section by variation of several parameters,namely the location (spacing 555 between), width 556, and depth 558 ofcuts (e.g. 544, 550) made. Wider spacing of cuts creates widertransverse beams, shallower cuts create wider axial beams. Likewise moreclosely spaced cuts create narrower transverse beams, and deeper cutscreate more narrow axial beams. Wider cuts create longer axial beams.The configuration of the micromachined tubing is defined by calculation,using well-known formulas for stress and stress/strain. The designprocess can further include finite-element analysis of the configurationto give localized stress and strain values. The calculations arerepeated as necessary using incrementally changing parameters tooptimize the design taking into account the concepts set forth herein.

Furthermore, another way of optimizing the design is to match, insofaras possible, the resistance to fatigue failure of the axial andtransverse beams. This can be modeled, and can also be determinedempirically. For example tubing samples can be spun in a tube having abend therein, counting the revolutions to failure. Examination afterfailure will show failure by crack propagation through an axial orthrough a transverse beam. The relative geometries can be adjusted tobalance the resistance to fatigue failure. Optimally the micromachinedtubing will fail at a corner between an axial and transverse beam, asstress concentration there will control if the resistance to fatiguefailure is sufficiently matched between the beam elements.

As a practical matter in manufacturing, a saw blade of a specified widthwill be used to make the cuts. And accordingly the width of all cuts isheld to this value. In the illustrated embodiment a diamond siliconwafer cutting saw blade (as is used in the microprocessor and memorychip manufacturing art—not shown) about one thousandth of an inch wideis used to make the cuts (e.g. 544). While it is possible to make widercuts by making a first cut, then moving the wire relative to the bladeby a distance up to a width of the blade, and repeating as necessary forwider cuts, speed of fabrication is higher if a single cut is used.Therefore, using this constant cut width, the possible variables aredepth 558 of cut and spacing 555.

Given that cut width 556 is to be held constant, in one embodiment theother parameters are selected as follows. The bending stiffness desiredat any selected location along a length of tubing is obtained byselection of an appropriate spacing 555 between cuts. Given that thewidth of cut is a constant, in the calculations, selection of a distancebetween the set of opposed cuts to be made (e.g. 546A) and the last setof opposed cuts made (e.g. 546) will define, by means of thecalculations, the depth of the cuts to be made as the distance betweencuts defines the width of the transverse beams, and the width of thetransverse beams is related to the width of the axial beam by thecondition of equality of strain values to be obtained for a givenapplied torsional force 554 as mentioned.

The locations of the axial beams 546 will be set by the relative angulardisplacement of the adjacent sets of opposed cuts, as will be described,and hence the width and the length of the transverse beams 552 will beknown. The width of the axial beams to be created depends on the depthof cut. The length of each axial beam is the same and equal to theconstant cut width (e.g. one thousandth of an inch in the illustratedembodiment). The depth of cut is determined by comparison of the strainin the each of the resulting axial beams (they are assumed to be thesame, though in fact they may not be in all cases due to differing forcedistribution due to variations in geometry) and then matching the strainin the axial beam(s) (e.g. 546) with the strain in the transversebeam(s) (e.g. 552). As will be appreciated, four transverse beams arecreated between each set of opposed cuts. The resulting strains areevaluated in each of the four beams, but in one embodiment anothersimplifying assumption is made that the strain in the two shortertransverse beams is the same, and likewise the strain in the two longertransverse beams is the same. The greater of the resulting strains inthe transverse beams is compared with the strain in the axial beams.This represents the force transmission path for transfer of the torque.The depth of cut 558 is varied until the strains are matched. This valueis then used in making the cuts at that location.

Other factors are taken into consideration. For example, there is apractical limit on the size of axial and transverse beams. Too large atthe desired advantages are lost, too small and imperfections inmaterials and variations within the tolerances in machining cancompromise performance. This may be governed by the thickness of thetubing if tubing is used, the size of the saw blade, accuracy of themachining apparatus, etc. Generally speaking, axial or transverse beamshaving dimensions on a par with or smaller than the width of the cuttingblade used to micromachine them are avoided.

Further refinement of the design can be by matching fatigue failureresistance as discussed above. Further reduction of opportunities fordevelopment of cracks in the material is desirable, and rounding of thecorners of the structure to reduce stress concentrations, and polishingof the structure, by electropolishing or abrasives as describedelsewhere herein, or some other method is desirable as it further roundscorners and polishes surfaces to reduce the probability of crackpropagation.

The design process then, in summary, is in one embodiment to space thecuts (e.g. 544, 550) apart along the axis 548 of the tubing so as toprovide bending as desired. The cuts will be closer together to giveless resistance to bending, and more spaced apart to give moreresistance to bending. (See, for example FIGS. 13 and 18, where thetubing segment 514 becomes more flexible toward the distal end 510 ofthe guidewire 500.) The stiffness can be controlled by means ofvariation of the spacing 555 of the cuts, the other parameters beingselected as appropriate as described above. The bending stiffness of thetubing can vary along the longitudinal axis, for example being made togradually become less stiff toward the distal end, by graduallydecreasing the spacing between cuts as in the above example.

As discussed, the depth 558 of the cuts is calculated usingstress/strain relationships to match the strain in the axial 546 andtransverse 552 beams created. In one embodiment as the calculationprogresses, the strain in the axial beams is matched to that of thegreatest calculated in the previously calculated transverse beams.Alternatively another method could be employed, for example comparingthe strain in a given axial beam 546A to that of the transverse beams552, 552A on either side of the axial beam along the axis 548 of thetubing 514 to match the strain. In another embodiment the average of thehighest strain values in transverse beams 552, 552A1, 552A2 (552A1 and552A2 being of unequal length the strains may be markedly different), oneither side can be used to match the strain in the axial beam 546A underconsideration. As will be appreciated, varying the thickness of theaxial beam(s) affects the forces transmitted to the transverse beams andtherefore varies the stress and strain in the transverse beam; so, as aresult, many iterations of these calculation steps can be required tooptimize the design. Likewise, adjustment of the size of one set ofaxial and transverse beams will affect the stresses and strains inadjacent sets of axial and transverse beams, so additional calculationsand re-calculations can be required to optimize by matching strainthroughout all the adjacent axial and transverse beams. Practicalconsiderations will require the use of a computer and appropriatealgorithm programed therein to optimize these design parameters. Again,refinement of the design by taking into consideration resistance tofatigue failure, or making this the primary design consideration areadditional approaches that can be taken.

With reference again to FIG. 20, the distribution of the orientation ofadjacent cut pairs giving rise to the axial beams 546 left after thecuts are made, will now be discussed. The object is to provide adistribution of cut orientations along the length of the tubing thatminimizes “preferred” bending directions of the micromachined tubing 514giving rise to undesirable effects collectively referred to as “whip” ora deviation of expected rotational result at the distal tip of theguidewire from that expected by the user from rotational inputs made atthe proximal end of the guidewire by turning the collet fixture 212.

With reference to FIG.22, one way of organizing the cut distribution tominimize whip is to assume a first cut pair of opposed cuts (180 degreesapart) and a second pair of opposed cuts immediately adjacent will beoffset by an angle of ninety degrees. Collectively the four cuts will bereferred to as a first cut set 560. A second cut set 562 of adjacentopposed cuts oriented ninety degrees apart is subsequently made, thesebeing oriented with respect to the first cut set (designated arbitrarilyas oriented at 0 degrees) so as to be rotated 45 degrees. The nextsimilar cut set 564 is oriented at 22.5 degrees, and the next at 67.5degrees, and so on in accordance with the distribution graphicallyillustrated in the figure. The sequence repeats every 64 cut sets (128opposed cuts, and 256 cuts in total).

With reference to FIGS. 23 and 24, in another embodiment, the cutdistribution is defined by a helical pattern. A first cut pair 570 is atzero degrees. A second cut pair 572 is rotated with respect to the firstthrough a chosen angle “x”. For example, this angle can be about 85degrees. A third cut pair 574 is oriented by rotation through an angleequal to 2x, or 170 degrees in the exemplary embodiment. This pattern iscontinued, as the next cut pair (not shown) is oriented at 3x or 255degrees, etc. continuing to turn in the same direction and by the samemagnitude of angular rotation, x. The bending axis 576 formed by thefirst cut pair 570 is oriented at 0 degrees; and the next bending axis578 formed by the second cut pair is oriented at 85 degrees in theexample, and the third bending axis 580 at 170 degrees, and so on. Thepattern will repeat after 72 cut pairs (144 total cuts) in theillustrated example where x is equal to 85 degrees. The orientation ofany pair of cuts (and hence the bending axis) will be given by thefollowing sequence: Pair 1=0 degrees; Pair 2=x degrees; Pair 3=2xdegrees; Pair N=(N−1)x degrees. Where the increment is 85 degrees thisis equivalent to 0; 85; 170; 255; . . . (N−1)85 . . . degrees. This hasbeen found to give good bending and torque transmission characteristicsand low whip. It also has the advantage of making the transverse beamsapproximately equal in length and this is advantageous in optimizing thedesign as will be appreciated.

With reference now to FIGS. 9, 10, 11 and 13 in comparing 0.014 inchdiameter Ni Ti tubing micromachined as disclosed herein to conventionalguidewire configurations and stainless steel tubing, it can be seen thatthe micromachined tubing is superior to conventional guidewireconfigurations when the diameter of the stainless steel core wire, whichconventionally transmits the great majority of the torque, drops belowabout 5 thousandths of an inch on the grind profile. Since no advantageis obtained when the core wire is this diameter and larger, there is noreason to provide micromachined tubing proximal of the point where thegrind profile drops to this value. Accordingly, for example in theillustrated embodiment it will be observed that where the medialsolder/glue joint (516 in the FIGs.) is located is substantially at thepoint where the grind profile drops to about 0.005 inch diameter. Asexplained, the NiTi tubing segment which has been micromachined asdescribed above provides a superior path for transmission of torque tothe distal tip 510 of the guidewire from that point while at the sametime facilitating bending. Thus the exemplary embodiment illustratesthat the guidewire configuration can be optimized for cost as well, theless expensive stainless steel core wire and conventional coilconfiguration being provided up to the point where bettercharacteristics are obtainable with a micromachined configuration.

Other features of the guidewire can include providing lubriciouscoatings on components distal of the proximal portion 502 previouslydescribed as including such a coating. For example a silicone coating asis known in the art can be applied in one of the many manners known inthe art.

Another feature is that the micromachined tubing can be deburred aftermicromachining if necessary. For example an acid wash etching processcan be used to deburr the inner surfaces, and the tubing can be placedon a mandrel and turned while being subjected to an abrasive jet todauber and round the micromachined edges to minimize the possibility ofcatching on anatomy.

In another aspect, the micromachining pattern can be altered to providepreferred bending directions. This can be useful in customizing theguidewire to reach a target location within a particular anatomicalstructure, or even a particular individual patient. As an example ofthis, a MRI or CAT scan can produce a data set from which a preferredaccess route, for example vasculature to a target site, can beconstructed in three dimensions. The guidewire can be micromachined toprovide locally variable flexibility as needed to facilitate thetraversing the last critical distance to the target site. A catheterindividually customized for that patent could be made from that data set(for example sent to the manufacturer via the Internet) and shipped outto the user very rapidly, since micromachining is a computer-controlledautomated process that could be customized based on the data set inaccordance with another automated procedure. This guidewire (or catheterfor that matter) could be individually identified by a bar code asdescribed herein.

As will be appreciated the guidewire 500 system in accordance withprinciples of the invention enables improved performance overconventional configurations, and can be optimized for cost andperformance. It is to be understood that the above-described exemplaryembodiments and arrangements are only illustrative of the application ofthe principles of the present invention. Numerous modifications andalternative arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the present invention andthe appended claims are intended to cover such modifications andarrangements.

What is claimed is:
 1. A guidewire system, wherein a guidewire isconfigured for introduction into a body lumen, comprising: a core wirehaving a proximal end, a distal end, and a tapering profile; amicromachined tube having a proximal end and a distal end, themicromachined tube being coupled to the core wire; a joint coupling themicromachined tube to the core wire; the location of the joint being ata location on the tapering profile where the torsional force which canbe transmitted by the core wire and the torsional force which can betransmitted by the micromachined tube are substantially the same.
 2. Aguidewire system as in claim 1 wherein the micromachined tube furthercomprises a plurality of axial beams and a plurality of transversebeams.
 3. A guidewire system as in claim 2, wherein the axial beams andthe transverse beams are configured so that a maximum torsional strainis substantially the same both in the axial beams and the transversebeams.
 4. A guidewire system as in claim 2, wherein the axial beams andthe transverse beams are configured so that a resistance to fatiguefailure is substantially the same in both the axial beams and thetransverse beams.
 5. A guidewire system as in claim 4, wherein themicromachined tube further comprises a polished surface.
 6. A guidewiresystem as in claim 4, wherein corners of the beams are rounded so as toreduce stress concentrations.
 7. A guidewire system as in claim 5,wherein the micromachined tube is electropolished.
 8. A guidewire systemas in claim 1, wherein the proximal end of the micromachined tube islocated adjacent the joint.
 9. A guidewire system as in claim 8, whereinthe core wire extends distally of the joint and the distal end of thecore wire is coupled to the micromachined tube.
 10. A guidewire systemas in claim 9, wherein the core wire and the micromachined tube arejoined at their respective distal ends.
 11. A guidewire system as inclaim 10, further comprising a plurality of axial beams and a pluralityof transverse beams configured so that a maximum torsional strain issubstantially the same in both the axial beams and the transverse beams.12. A guidewire system as in claim 11, wherein resistance to fatiguefailure is substantially the same in the axial and transverse beams. 13.A guidewire system as in claim 1, further comprising a coil disposedbetween the core wire and the micromachined tube.
 14. A guidewire systemas in claim 1, wherein the micromachined tube is configured so itslateral flexibility varies with position along its length.
 15. Aguidewire system as in claim 14, wherein the flexibility of themicromachined tube increases toward its distal end.
 16. A guidewiresystem as in claim 14, where the flexibility of the micromachined tubesequentially increases, then decreases, then increases with a change inposition along its length.
 17. A guidewire system as in claim 1, whereinthe joint is located intermediate the proximal and distal ends of themicromachined tube.
 18. A guidewire system as in claim 1, wherein theguidewire further comprises a proximal coil having a proximal end and adistal end, the proximal coil being disposed over the core wire andcoupled thereto at the proximal end of the proximal coil, at least aportion of the proximal coil being disposed proximally of themicromachined tube.
 19. A guidewire system as in claim 18, wherein atleast a portion of the proximal wire adjacent its distal end is disposedbetween the micromachined tube and the core wire.
 20. A guidewire systemas in claim 19, further comprising a medial coil, said medial coilhaving a proximal end and a distal end, said medial coil being disposedbetween the micromachined tube and the core wire.
 21. A guidewire systemas in claim 20, wherein the medial coil has an unwound portion adjacentits proximal end and the proximal coil has an unwound portion adjacentits distal end, said unwound portions of the respective medial andproximal coils overlapping and being wound together to provide amechanical interlock between the proximal coil and the medial coil, themicromachined tube overlaying the overlapping portions.
 22. A guidewiresystem as in claim 21, where the overlapping portions are locatedadjacent the joint.
 23. A guidewire system as in claim 22, furthercomprising a distal coil, the distal coil being coupled to the medialcoil and to the core wire, the distal coil being disposed between thecore wire and the micromachined tube.
 24. A guidewire system as in claim1, wherein the core wire has a first outer diameter along a substantialportion of its length, and the micromachined tube has an outer diametersubstantially the same as the first outer diameter of the core wire overat least a portion of its length.
 25. A guidewire system as in claim 1,further comprising a proximal coil disposed over the core wire proximalof the micromachined tube, the core wire having a first outer diameteralong a substantial portion of its length, the proximal coil havingsubstantially the same outer diameter as the first outer diameter of thecore wire, and the micromachined tube having substantially the sameouter diameter as the proximal coil.
 26. A guidewire system, wherein aguidewire is configured for introduction into a body lumen, comprising:a core wire having a proximal end and a distal end and a taperingprofile including a transition where a diameter of the core wire changesfrom a first outer diameter proximally to a second smaller outerdiameter distally; a micromachined tube having a proximal end and adistal end, the micromachined tube being coupled to the core wireadjacent the transition; a joint coupling the micromachined tube to thecore wire; a location of the joint being adjacent the transition, andwherein the torsional force which can be transmitted by the core wireand the torsional force which can be transmitted by the micromachinedtube are substantially the same adjacent the joint.
 27. A guidewiresystem as in claim 26, wherein the core wire has a first outer diameterproximal of the joint and wherein the micromachined tube has an outerdiameter substantially the same as the first outer diameter.
 28. Aguidewire system as in claim 26, wherein the guidewire further comprisesa proximal coil having a proximal end and a distal end, and the corewire having a proximal transition located proximal to the transitionadjacent the joint, the proximal end of the proximal coil being coupledto the core wire adjacent the proximal transition and the distal endbeing adjacent the joint, whereby the outer diameter of the guidewire issubstantially the same along the guidewire.
 29. A guidewire system as inclaim 27, wherein the proximal coil further comprises a portion adjacentits distal end having a smaller outer diameter than the first outerdiameter, the micromachined tube overlying at least a portion of theproximal coil adjacent the distal end of the proximal coil.
 30. Aguidewire system as in claim 26, wherein the micromachined tube furthercomprises a plurality of axial beams and a plurality of transversebeams.
 31. A guidewire system as in claim 29, wherein the axial beamsand the transverse beams are configured so that a maximum torsionalstrain is substantially the same in both the axial and the transversebeams.
 32. A guidewire system as in claim 29, wherein the axial beamsand the transverse beams are configured so that a resistance to fatiguefailure is substantially the same in the axial and the transverse beams.33. A guidewire system as in claim 31, wherein the micromachined tubefurther comprises a polished surface.
 34. A guidewire system as in claim29, wherein the corners of the beams are rounded so as to reduce stressconcentrations.
 35. A guidewire system as in claim 26, wherein the corewire extends distally of the joint and the distal end of the core wireis coupled to the micromachined tube.
 36. A guidewire system as in claim34, wherein the core wire and the micromachined tube are joined at theirrespective distal ends.
 37. A guidewire system as in claim 26, furthercomprising plurality of axial beams and a plurality of transverse beamsconfigured so that a maximum torsional strain is substantially the samein the axial and the transverse beams.
 38. A guidewire system as inclaim 37, wherein resistance to fatigue failure is substantially thesame in the axial and transverse beams.
 39. A guidewire system as inclaim 26, wherein the micromachined tube is configured so its lateralflexibility varies with position along its length.
 40. A guidewiresystem as in claim 26, wherein the guidewire further comprises aproximal coil having a proximal end and a distal end, the coil beingdisposed over the core wire and coupled thereto at the proximal end ofthe proximal coil, at least a portion of the proximal coil beingdisposed proximally of the micromachined tube.
 41. A guidewire system asin claim 28, further comprising a medial coil, said medial coil having aproximal end and a distal end, said medial coil being disposed betweenthe micromachined tube and the core wire.
 42. A guidewire system as inclaim 41, wherein the medial coil has a proximal unwound portionadjacent its proximal end and the proximal coil has an unwound portionadjacent its distal end, said unwound portions overlapping and beingwound together to provide a mechanical interlock between the proximalcoil and the medial coil, the micromachined tube overlaying theoverlapping portions.
 43. A guidewire system as in claim 42, where theoverlapping portions are located adjacent the joint.
 44. A guidewiresystem as in claim 43, further comprising a distal coil, the distal coilbeing coupled to the medial coil and to the core wire, the distal coilbeing disposed between the core wire and the micromachined tube.
 45. Aguidewire system, the guidewire being configured for guideablytraversing a body lumen, comprising: a core wire having a proximal end,a distal end, and an outer diameter, and a transition intermediate theproximal and distal ends where the outer diameter changes from a largerdiameter proximally to a smaller diameter distally; a micromachined tubehaving a proximal end and a distal end, said micromachined tube furthercomprising a plurality of axial beams and a plurality of transversebeams, the beams being configured so that resistance to fatigue failureof the axial beams and of adjacent transverse beams is substantially thesame, the micromachined tube being disposed over the core wire andcoupled to the core wire adjacent the transition; the core wire having acapacity to transmit torsional force that is substantially the same as acapacity to transmit torsional force of the micromachined tube adjacentthe transition; whereby the capacity of the guidewire to transmittorsional forces is substantially maintained from that of the core wireproximal of the transition to that distal of the transition where thecore wire has a smaller outer diameter and at least a portion of thetorsion forces are carried by the micromachined tube.
 46. A guidewiresystem as in claim 45, wherein the core wire extends distally of thetransition to the distal end of the micromachined tube and wherein themicromachined tube is coupled to the core wire adjacent the distal endof each.
 47. A guidewire system as in claim 46, further comprising aproximal coil having a proximal end and a distal end, the proximal coilbeing disposed over the core wire proximally of the micromachined tube.48. A guidewire system as in claim 47, further comprising a proximaltransition, and wherein the proximal end of the proximal coil is coupledto the core wire adjacent the proximal transition, and the distal end ofthe proximal coil is coupled to the core wire adjacent the transitionwhere the micromachined tube is coupled to the core wire.
 49. Aguidewire system as in claim 48, wherein an outer diameter of theguidewire is not substantially increased along the length thereof fromthe proximal end to the distal end.
 50. A guidewire system as in claim45, wherein the axial beams and the transverse beams are configured sothat a maximum strain occurring in either of the axial or transversebeams from torsion and bending forces is substantially the same.
 51. Amethod of enhancing performance of a coronary guidewire is given byundertaking steps comprising: providing a micromachined tube, said tubehaving a plurality of axial beams and a plurality of transverse beams;configuring the micromachined tube so that a maximum strain induced inthe axial beams from torsion and bending of the micromachined tube issubstantially the same as that in the transverse beams; providing a corewire having a diameter profile and a transition from a first diameterproximally to a second smaller diameter distally, coupling themicromachined tube to the core wire adjacent the transition; selectingdiameters of the profile and the position of the coupling of themicromachined tube to the core wire so that a torque transmissioncapacity of the core wire is substantially the same as a torquetransmission capacity of the micromachined tube adjacent the location ofthe coupling.
 52. A guidewire system wherein improvement of performanceof a coronary guidewire is given by undertaking steps comprising:providing a micromachined tube, said tube having a plurality of axialbeams and a plurality of transverse beams; configuring the micromachinedtube so that resistance to fatigue failure of an axial beam from torsionand bending of the micromachined tube is substantially the same as anadjacent in transverse beams; providing a core wire having a diameterprofile and a transition from a first diameter proximally to a secondsmaller diameter distally, coupling the micromachined tube to the corewire adjacent the transition; selecting diameters of the profile and theposition of the coupling of the micromachined tube to the core wire sothat a torque transmission capacity of the core wire is substantiallythe same as a torque transmission capacity of the micromachined tubeadjacent the location of the coupling.
 53. A guidewire system as inclaim 52, further comprising the step of rounding corners of the axialand transverse beams.
 54. A guidewire system as in claim 53, furthercomprising the step of polishing the micromachined tube.